Ceramics of the melilite‐type compound La1+xSr1−xGa3O7−δ were prepared by conventional ceramic processing. Samples prepared represented the entire homogeneity region of the phase (i.e., x=−0.15 to 0.60). Electrochemical characterization under variable temperature and atmospheric conditions in the vicinity of air entailed four‐point direct‐current conductivity measurements and electromotive force measurements. La1+xSr1−xGa3O7−δ samples exhibited a p‐type behavior with generally increased conductivity with increased substitution of lanthanum for strontium, which reached a saturation value of ∼10−1 S·cm−1 at 950°C.

The ternary systems La2O3–SrO–Ga2O3, La2O3–MgO–Ga2O3, and SrO–MgO–Ga2O3 were studied at 1400°C in air, with emphasis on LaGaO3. The compound exhibited a small solid solubility of strontium substituting for lanthanum and also of magnesium substituting for gallium. In the system La2O3–SrO–Ga2O3, LaGaO3 existed only within a very narrow concentration region, whereas in the system La2O3–MgO–Ga2O3, LaGaO3 was in equilibrium with most of the phases of the system. The system SrO–MgO–Ga2O3 at 1400°C in air was characterized by an extended liquid phase at ∼1185°C.

The quasi binary systems LaMnO3–SrMnO3 and LaMnO3–CaMnO3 were studied. Both systems show a miscibility gap at intermediate La:Sr and La:Ca ratios below about 1400 °C in air. This phenomenon causes the decomposition of single-phase (La,Sr)MnO3−x and (La,Ca)MnO3−x solid solution into La-rich SrMnO3−x + Sr-rich LaMnO3−x and La-rich CaMnO3−x + Ca-rich LaMnO3−x at lower temperatures, respectively. At 1400 °C in the system LaMnO3–SrMnO3, a structure transformation of (La,Sr)MnO3 from orthorhombic to rhombohedral with increasing Sr content was not observed, and the structure of La0.7Sr0.3MnO3 was determined to be orthorhombic with a = 0.54927 ± 0.0009 nm, b = 0.54582 ± 0.0009 nm, and c 4 0.76772 ± 0.0034 nm.

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Powders of LaGaO3, La0.9Sr0.1GaO2.95 and La0.8Sr0.2Ga0.83Mg0.17O2.815 were prepared by the amorphous citrate/EG method. The calcination behavior of the precursor powders of the above phases were studied in the temperature range of 200°-1400°C, in an air atmosphere. Characterization of the samples were performed by XRD, TG/DTA, FTLR, SEM, ICP-AES, and carbon and nitrogen analyses.